In recent years the cylinder lock has been used in virtually all key-type lock assemblies. Such a lock comprises a sleeve mounted in the lock housing, and a plug rotatable in this sleeve by means of a key. The tumblers between the shell and the plug allow this plug to be rotated only when a key having appropriate bittings is fitted into the plug. A tongue or pawl carried on this plug serves to operate the locking element within the lock assembly.
Such a lock has been developed to a high degree, with tubular-type keys, magnetic keys, and similar arrangements almost making the lock pickproof. Furthermore the use of new extremely hard metals has made it almost impossible to drill out such a lock to forcibly open it. The key for such a lock is usually small and convenient to carry.
It has been found, however, that in most break-ins or burglaries where a cylinder lock is forced a crude but simple method is used. The bezel ring is pried away from around the cylinder and a wrench is locked on to the shell of the cylinder lock. The cylinder itself is then turned and ripped physically out of the lock assembly so as to expose the internal mechanism which can usually be operated by means of a screwdriver.
In maximum-security arrangements, such as safety deposit boxes, bank vaults, strongboxes, and the like it is known to provide a tumbler-type lock. A bulky key that is relatively expensive to duplicate has a bitting that coacts directly with several tumblers well within the lock structure so as to displace these tumblers into an aligned position that allows a locking element to be displaced. Since all of the operating mechanism is well within the lock and the bitting necessary to move these tumblers into the requisite aligned position is extremely difficult to ascertain, such a lock is not only pickproof but very difficult to force. By the same token such a lock is also quite expensive and, therefore, not adapted to general use.